Supernatural is going to get a big jolt of nerd cred with the
recent casting of Felicia Day. The actress will appear in the April 27
episode "The Girl with the Dungeons and Dragons Tattoo." Day will play
Charlie, a computer hacker working at a company owned by Leviathan boss
Dick Roman.

While Felicia Day may not be a household name, she's an icon to hardcore Internet fanboys for her work on the web and in the Whedonverse. To help get you up to speed, here's a look at Day's five greatest, nerdiest roles.

#5 vi on Buffy the Vampire Slayer

In the final season, Day launched her cool career as one of the Potentials who joined Buffy and company.

#4 Mag on Dollhouse

When Joss Whedon finds an awesome, talented actress, he keeps using her again and again, which is what happened when Day showed up in the post-apocalyptic future on Dollhouse.#3 Dr. Holly Marten on Eureka

Day's most recent role is as an adorable genius on Syfy's Eureka. Fans can see her again when the show returns for its fifth and final season on Monday, April 16.

#2 Penny in Dr. Horrible's Sing-a-Long Blog

Day's third collaboration with Joss Whedon, she showed off a great singing voice and co-starred with Neil Patrick Harris and Nathan Fillion in this iconic musical web miniseries.

#1 Codex in The Guild

If there's one role that defines Day's geek cred, it's as the writer, creator and star of this brilliant web series about a group of people who play an online role-playing game together. Check it out HERE.

Are you excited to see Felicia Day on Supernatural? What's your favorite role of hers?